Coating machine having spiral surface agitator roll



52 us. Cl

United States Patent 72] Inventors William Galloway Osborne, Jr., and

Howard Ivan Wilson, Towanda, Pennsylvania 21 Appl. No. 754,014

[22] Filed Aug. 20,1968

[45] Patented Nov. 17, 1970 [73] Assignee E. I. du Pont de Nemours and Company Wilmington, Delaware a corporation of Delaware [54] COATING-MACHINE HAVING SPIRAL SURFACE AGITATOR ROLL 5 Claims, 3 Drawing Figs.

[51] Int. Cl B05c 1/08 [50] Field of Search l 18/258, 249, 259; 101/315, 321, 326, 340, 344

[56] References Cited UNITED STATES PATENTS 3,097,968- 7/1963 Schaefer 118/259 3,106,480 10/1963 Baker ll8/259X Primary Examiner-John P. McIntosh Attorney-Lynn Barratt Morris ABSTRACT: A top feed roll coating machine having an agitating roll with a spirally grooved surface of opposite direction from the center to the ends mounted between the coating roll and metering roll. Said agitating roll is driven and is capable of facilitating streak-free plate, sheet or web coatings.

Patented Nov. 17, 1970 3,540,410

SHEET 1 OF 2 WILLIAM GALLOWAY OSBORNE, JR. HOWARD IVAN WILSON ATTORNEY I Patented Nov. 17, 1970 3,540,410

SHEET 2 of 2 Fl G- 3 INVENTORS WILLIAM OALLOIIIAY OSBORNE, JR. HOWARD IVAN WILSON BY ATTORNEY COATING MACHINE HAVING SPIRAL SURFACE AGITATOR ROLL BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll coating process and machine. It more particularly relates to a top feed, multiroll uniform coating process and machine for coating plates or webs.

2. Description of the Prior Art Various roll coating machines are known. The web or plate may move in the direction of the rotating coating roll, i.e., reverse roll coating. The rolls may consist of metal, nonmetal or covered metal rolls. Metal rolls produce electrostatic effects and nonuniform caliper gives less desirable coatings unless the rolls have resilient surfaces. In reverse roll coating, if the surface of the web or plate is pliable, more uniform coating may be achieved regardless of the caliper ofthe support.

Where multiroll machines are used, the sheets or webs are subjected to pressure between rolls during coating. Accordingly, nonuniform coating may occur as the result of roll deflection, nonuniform dispersion of coating solution during transfer from the roll, etc.

Nonuniformity resulting in streaky coatings is a major problem and is characteristic of top feed roll coaters. Streaking is produced by the continuous reverse flow of the circular motion of the solution in the feed nip with respect to the direction of the coating roll. Disruption of the continuously flowing solution at regular intervals causes eddies which result in streaks in the final coating. Where wide coating machines are involved and rolls large in diameter are necessary, coarse ribs are present in the final coating. These coarse ribs which are more defined streaks or coating weight bands result from the larger angle tangent to the roll. Coarse ribs are reduced by means of smaller rolls rotating in the same direction at lesser speeds and providing a lesser angle of tangent.

Conventional machines for coating plates, sheets, or webs are vibrated often. The driven and/or nondriven rolls may be vibrated and the coating solution kept in suspension. High frequency vibration of the solution container to eliminate bubbling is known.

The machine of this invention substantially eliminates eddy formation; provides continuous uniform coatings, and overcomes streaking or coarse rib problems.

SUMMARY OF THE INVENTION This invention comprises an agitated top feed multiroll coating machine comprising a nip agitator roll, a top feed station, and a solution recirculation system. The agitator is a roll or bar which may or may not be rotated in the feed nip area. Said agitator, which effectively disrupts eddy formation, spans the full width of the solution reservoir between the coating and metering rolls.

More particularly, the sheet or web coating machine comprises (I) a metering roll, (2) an adjacent transfer roll adapted to receive a coating solution in the nip area between the rolls, (3) plates at the ends ofthe rolls, (4) an agitator roll extending between said end plates and located in said nip area to be immersed in the coating solution supplied to said area, said agita tor roll having grooves or ridges on its outer surface starting near the center of the roll and extending in spirals of opposite direction to the ends of said roll, (5) a sheet support roll beneath said transfer roll and adapted to receive a sheet or web to be coated in the nip between said rolls, and (6) a lateral supply conduit disposed above said roller for supplying coating material to said nip area.

DESCRIPTION OF THE PREFERRED EMBODIMENT The agitator roll is a driven roll or bar positioned in the nip between and in close proximity to the coating and metering rolls so that the agitator will be immersed in the solution reservoir formed by the nip between said rolls. Said roll may be metal, plastic or any rigid material and preferably has a threaded or grooved surface or ridges similar to that of a double helix. According to the present invention, a grooved metal, e.g., stainless steel roll of small diameter is provided with grooves forming a double helix extending from the center to the ends ofthe roll.

The coating composition is fed into the nip through trans verse pipe or conduitjust above the nip agitator roll. The pipe or conduit which extends the full width of the nip area has a narrow slot or a plurality of perforations and closed ends. Solution is introduced into an intake opening and flows through the outlet or outlets into the space between the rolls. The coating solution can be circulated from the space to a supply reservoir and returned to the distribution pipe or conduit.

The recirculation system can have a combined gravity-feed, filter pump transfer system. Solution remaining on the coating roll after coating a sheet is picked up by a doctor roll, removed therefrom by a doctor blade and allowed to flow to a pan. An inclined pan may span the width of the rolls and be provided with a drain to an outlet or to a tank for recirculation.

The paper. metal sheet, plate, or web or other support to be coated is passed between coating and backup rolls by the motion of the two driven rolls. Solution transfer from the coating roll onto the support material occurs at the contact point. Pressure at the point is regulated so as to produce the desired coating thickness.

The primary advantage of the present invention is that it provides a practical machine by which coating streaks caused by eddies may be eliminated.

Another advantage is that the machine provides for controlled supply of coating solution. Uniform dispersion of coating solution may be achieved by the spreader roll located near the center ofthe nip.

It is an object of this invention to provide a machine for mildly agitating and spreading a solution in the feed nip reservoir ofa multiroll coater.

A further object is to provide improved means for equally distributing the coating solution on the coating roll. A still further object is to provide a means for controlling the flow rate of coating. Other objectives are to provide a recirculation system for excess coating material.

DESCRIPTION OF DRAWINGS FIG. I is an isometric view of the machine showing the rolls, reservoir at the nip and the agitator roll.

FIG. 2 is an isometric view of the agitator roll and support mechanism with parts in broken section.

FIG. 3 is a schematic isometric view of the roll assembly with the recirculation system.

With reference to the drawings which constitute part of this application, the same reference numerals refer to the same parts throughout the several views.

As shown in FIG. 1, the coating machine of this invention is provided with a supply pipe or conduit 26 to supply solution and an agitator roll 10 beneath the conduit to spread and mildly agitate the solution. The agitator roll is mounted below the conduit in the nip between coating roll 11 and metering roll 12. Backup roll 13 is below roll 11 and below roll 10. Supports 22-23 at the end of theagitator roll also serve as ends for the reservoir for the coating solution between the rolls.

Although the agitator roll 10 is in close proximity to the coating roll 11 and metering roll 12, clearance is not exact. Tolerances are set so as to allow total immersion of the agitator roll 10 in the coating solution reservoir R. Clearance settings which allow thorough rotary mixing by the agitator roll 10 and permit proper transfer to the coating roll 11 are adequate.

The coating roll 11 is a driven roll with a resilient surface, e.g., rubber covered, stainless steel roll of large diameter which rotates clockwise, while the backup and metering rolls rotate counterclockwise. The metering roll 12, along with the coating roll 11, and the end plates or dams 18-19, form the solution reservoir R. It is necessary that tolerances between the metering roll 12 and the coating roll 11 permit solution passage yet be close enough to decrease the effect of a nonconcentricity on the coating roll 11. In instances where settings between the metering roll 12 and the resilient coating roll 11 are very close, the compression between the two rolls and the hydrodynamic force created by the solution facilitate proper solution flow.

Upon introducing sheets M to be coated between rolls 11 and 13, and while supplying coating material through perforations 34 in conduit 26, coating material is transferred to the surface of the sheets to form a uniform coating. Solution from the reservoir R adheres to the coating roll 11 and is transferred to the sheet or web M at the force nip N formed therein with the backup roll 13. The backup roll 13 which is of close proximity to the coating roll 11 provides sufficient pressure on the resilient roll to just accommodate the passing solution layer and sheet material M. The excess of solution which adheres to the coating roll 11 and is not applied to the support material M is transferred onto the doctor roll 14 and shortly removed by the doctor blade 28 into a catch pan 29 as shown in FIG. 3.

Referring to FIG. 2, this embodiment of the machine comprises a stainless steel agitator roll of small diameter spanning the entire width of the web and having a partially grooved or threaded surface. The agitator roll 10 is positioned just below the feed station 26 and above the coating roll 11 and metering roll 12 (FIG. 1) and is supported at both ends by mechanisms comprising a copper bushing 16 with a support bearing 17 attached to end dams 18, 19 with dam liners 20 and 21 at each end.

In greater detail, the rotatable agitator roll 10 is supported at one end by the seal block 23 while the opposite driven end extends through the seal block 22 to the timing belt pulley 24.

In accordance with the present invention, the supply conduit 26 is a plastic tubular structure suspended by two adjustable end clamps 35 and 36. Said feed station 26 is located immediately above the agitator roll 10 and the respective solution reservoir R formed therein. The supply conduit 26 is sealed at both ends and provided with an upper inlet 27 located at the center ofthe conduit.

As shown in FIG. 3, the recirculating system consists of a hold tank 30, pump 31 and filters 32, 33 interconnected by tubing from the catch pan 29 to the supply conduit. The holdtank 30 which is gravity fed from the catch pan 29 may be any suitable container. Solution is then pumped from the holdtank 30 by the displacement rotary pump 31 through pipes or tubes, control valves 37 and 38, and two inline filters 32, 33, and eventually to the supply intake 27.

The rolls can be driven by means of a motor or motors and suitable belts and pulleys and chains or sprockets or gears (not shown) as is common in coating machines. Rolls 11, 12, and 13 may be driven in synchronism and roll 10 can be driven independently or in synchronism with the other rolls.

Coatings obtained from a top feed roller coater are dependent on many variables. Some of the most significant variables which determine final coating quality are the rheological properties of the coating solution, dimensions of the apparatus, tolerance of the roll settings, receptivity of material to be coated, and actual coating speed of the machine. Factors such as dimensions of the apparatus, tolerances of roll positioning, and actual speed of the machine are effective but may be dependently adjusted with various coatings and support materials. However, rheological properties, particularly viscosity, are dependent on machine adaptability which is reflected in final coating.

The spreader rolls may have helical grooves having a depth surface of the roll.

EXAMPLE A coating solution sample was prepared and coated in a machine, as described above, but without the spreader roll.

A photopolymerizable composition comprising essentially a 35 percent total solids mixture of polymethylmethacrylate/methacrylic acid 6.2 parts, pentaerythritol triacrylate 4.0 parts, and triethyleneglycol diacrylate 1.3 parts, mixed with amounts of photoinitiator and a blue dye in 2-ethoxy ethanol was coated on a brush grained, unheated aluminum plate. Streaking in the direction of the applied coating occurred.

An agitator roll copper wire having a diameter of one-sixteenth inch wrapped around the roll in the form of two helixes starting near the center and continuing in opposite direction to the ends of the roll.

The coaxial movement of the metering roll and the coating roll along with that of the agitator roll provided the sufficient mechanical energy necessary to disrupt eddy formation. The resultant coatings were free from streaks and were of good uniform qualityv In practical machines, rolls I2 and 13 can be 6 to ID inches, roll 11, 6 to 10 inches, roll 10 /2to 1 inch, and doctor roll I to 6 inches in diameter. The speed of rotation will vary depending upon the viscosity of the coating compositions. Roll 11 may turn at 15 to 60 r.p.rn., and roll 10, 10 to rpm.

The various rolls and associated parts will usually be made of corrosion-resistant metals or metal alloys, e.g., copper, bronze, steel, stainless steel, ion-nickel alloys, etc. The other associated parts can be made of the same and other materials. In some instances, parts can be made of tough, chemically-resistant resins or plastic materials. Metal rolls can be coated with hard resins or plastic materials, e.g., phenol formaldehyde, melamine, polyaldehyde, etc., resins, polytetrafluoroethylene, etc.

Roll 11 may have a noncorrosive resilient surface of rubber or a synthetic elastomer, polysilicone, or polyethylene.

We claim:

I. A sheet or web coating machine comprising:

1. a metering roll;

2. an adjacent transfer roll adapted to receive a coating solution in the nip area between the rolls;

3. plates at the ends of the rolls;

4. an agitator roll extending between said plates and located in said nip area to be immersed in the coating solution supplied to said area, said agitator roll having grooves or ridges on its outer surface starting near the center of the roll and extending in spirals of opposite direction to the ends ofsaid roll;

. a sheet support roll beneath said transfer roll and adapted to receive a sheet or web to be coated in the nip between said rolls; and

6. a lateral supply conduit disposed above said roller for supplying coating material to said nip area.

2. A machine according to claim 1 having means for rotating each of said rolls.

3. A machine according to claim 1 having means for supplying coating material to said supply conduit and means for circulating coating material from the nip area to said conduit.

4. A machine according to claim 1, wherein the transfer roll has a resilient surface.

5. A machine according to claim 1 having a doctor roll coacting with said transfer roll and means for removing excess coating material from said doctor roll. 

